Protective arrangement



O. C. TRAVER PROTECTIVE ARRANGEMENT Filed Narchll 19,26

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His AT1" Patented. Feb. 21, 1928.

UNllltDy STATES PATENT oFFIcEQ OLIVR G. TRAVER, OF SCHENECTADY, NEW YORK, ASSIGNGB TO GENERAL ELECTRIC COMPANY, A CORPORATION 0F NEW YORK.

PROTEGTIVE ARRANGEMENT.

Application led March 1S, 1926. Serial no. 95,757. E l

My invention relates to improvements in protective arrangements for electric system and more particularly for systems comprising two parallel lines, especially when these are provided with a dilierential system of protection involving current transformers which are connected in series for normally circulating current, whereby further protection, such that either line alone may carry as l@ much current as the two together, is provided in an economical and satisfactory manner.

My invention will he better understood from the following description taken .in l@ connection with the accompanying drawing,

and its scope will he pointed out in the appended claims.

ln the accompanying drawing, Fig. 1 illustrates diagraatically, in single phase 2@ 'for clearness, an embodiment oi my invention as appliedto two parallel lines provided with a dierential system ot protection, and Figs. 2 and 3 illustrate da rammatically, also in singlephase, modiiications oi the emloodiment of my invention shown in llig. 1.V

ln the several iigures oi the drawing, two parallel lines, l and 5, of which onl one phase conductor as shown, are arrange to be connected to a bus through suitable circuit interrupters 7 and 8 having trip coils 9 and 10. For selectively controlling the opening oit the circuit interrupters 7 and 8 on the occurrence ot faults, there may he provided a dierential protective arrangement which is herein shown as comprising an over-current relay 11 having a coil -12 and a directional relay 13 having cooperating current and potential coils` 1a and 15 respectively. 'lhe directional relay 13 has two sets ot contacts, 16 and 17 which are connected in series with the trip coils 9 and 10 respectively and in series with the contacts 18 of theover-current relayA 11. 'lhe potential coil 15 of the directional relay 13 is arranged to be ener gized from the lous 6 through a potential transformer 19. ln order that the coil 12 of the over-current relay 11 and the current coil lll oi the directional rela 13 may he energized in accordance with t e vectorial dierence between the currents in corresponding phase conductors ot the lines and 5, they are connected 'between points 20 and 21 of a circuit comprising the secondaries 22 and 23 of current transformers energized respectively irom the lines 4 and 5, the secondaries 5% being connected in series for normally circulating current. These points 20 and 21 are so chosen that with the lines d and 5 carrying currents in the same direction and the current transformer secondaries 22 and 23 furnishing substantially equal currents, the points are at substantially the same potential and this is what is meant hy the" expression norsrnally at substantially the same potentia A protective arrangement of this type, as is well known, will operate selectively in accordance with the magnitude and direction f oi the vectorial dierence between the currents in the lines e and 5 to control the circuit interrupter in the line carrying the greater current. lt is irequently desirable, however, to protect the lines a and 5, not only in accordance with the vectorial diierence between the line currents hut also in accordance with the vectorial sum of the line currents, in such a manner that either one of the lines alone, when the other is out of service, may carry as muchcurrent as thev two vlines together without the necessity or readjusting any of the protective apparatus. ln accordance with my invention, l accomplish this hy an inductive means 24e, oomprising an'inductive winding which is connected inthe circulating current circuit ot the current transformer secondaries 22 and 23 and which includes at anintermediate point one o the points 20 and 21 inthe connection across the normally circulating current circuit. Jassociated ywith the inductive means and arranged to he energized theretrom is an electroresponsivedevice such as an over-current relay 25 which has an energizing coil26 and which is arranged to control the circuits oi2 the trip coils 9 and 10 through contacts 27.

ln lig. 1, the inductive means 2liis illustrated as a stationary inductive means comprising an inductive winding' 28 across which the relay coil 26 is connected. With loo current will flow in the connection between f the points andv21, since they have substantially the same potential under the conditions assumed. Consequently, the inductive winding 28 acts in efect asa reactor and a current substantially equal to onehalf of the sum of the currents in the current transformer secondaries 22 and-23, that is, proportional to the suml'offthe` line currents, appears in the relay coil 26. When this current exceeds thatv for which the relay 25 vis set tooperate,both ofthe circ-uit interrupters 7 and48 Will be tripped.v` If the current in one line, kfor example, line 4,- 1s greater thanthe current in the line 5 then a current proportional to the current 1n the line 4 tends to flow through one-half of the vinductive winding l28 while aj current proportional to the current in' the line 5 tends to How through lthev other'half'in" the rsame direction. The` dierence between these currents appears inthe `connection between the points 2O and 21, since they are not.- at substantially the same' potential. One-half of this difference flows in one direction in V,one-half of the winding 2,8 and the other half of the difference flows in the opposite direction in the other half of the winding 28. Consequently this winding 28 acts in effect asa reactor and a current substantially equalto one-half of the vectorial sum of the A currents in the current transformer secondaries 22 and 23 appears in the relay 'coil 26 and the circuit interrupters 7 and 8 will be tripped when this current exceeds the predetermined value for which the relay is set to operate. If one line, for example, line 5, is out of service, then theyinductive winding 28 acts in effect as an auto-transformer with a 1 to 2 turn ratio, one-half of the winding being energized by a current proportional to the current in the line 4 and acting as the common winding while the other half of the winding acts as the series winding. Consequentlyl the current in the relay coil 26 is substantially proportional to the vectorial sum of the currents in the two lines, since the current 'in line 5 is, by)

assumption, zero. In this case, when the current in the relay coil 26 exceeds the predetermlned value, the circuit interrupter 7 will be tripped. Thus the relay 25 is always energized by a current proportional tov vectorial sum of the line currents, whetherl one or two lines are'in service and therefore either line, when in service alone, may be operated at substantially the same current as the two lines together without changing the relay adjustment.

In the previous cases of operation discussed, it has been assumed that the currents in the two lines are in the same direction, but the relative direction of these currents is immaterial so far as energizing the' relay 25 by a current proportionalto the vectorial sum of the line currents is concerned.- Thus assuming, that each of the lines is carrying the same current but that these currents are flowing in opposite directions, then the inductive winding 28 acts in effect as a balanced end reactor, that is a current proportional to the current in the line 4 ows 1n one direction in one-half of the 'winding 28 and an equal current proportional to the current in the line 5 liows in the opposite direction in the other half of the winding 28. These currents combine and flow through the connection between the points 20 and 21 and the inductance of the winding 28 is` substantially zero, so that substantially no current flows in the relay coil 26. This is as it should be, for the vectorial sum of two equal and opposite currents, as assumed, is zero.

In Fig. 2, the inductive means 24 is illustrated as mutually inductive in the form of a transformervwhose primary 29 is connected in the same manner as the inductive winding 28 of Fig. 1, as heretobefore described, and whose secondary 30 has in circuit therewith the relay coil 26. With this' arrangement,

Iif we assume, for example, that the ratio of the turns in the winding 29 to the turns 1n th'e winding 30 is 2 to 1, then the relay coil 26 will befenergized by a current which readily be understood, since one half of the'` winding 29 will be energized by a current substantially equal to the current in the cur'- rent transformer secondary 22 and the vother half by a current substantially equal to the current in the current transformer secondary 23. The resultanteii'ect of the winding 29 is therefore substantially equal to one-half the ,vectorial sum of the currents in the current transformer secondaries 22 and 23, that is proportional to the vectorial sum of the line currents. This resultant eect or sum, by reason of the transformation ratio assumed, appears in the secondary winding 30, and therefore the relay coil 26, as a current substantially equal to the vectorial sum of the currents in the current transformer secondaries 22 and 23, that is, proportional to the vectorial sum of the line currents.

In Fig. 3, the inductive means 24 is illustra-ted as comprising the winding 3l connected in the same manner as the inductive winding 28 of F ig, 1, as heretofore described. In this modiiication, the relay coil 26 is shown as Connected between the quarter points of the .inductive winding 31. This winding actsin effect as a l to 2 turn ratio auto-transformeinmm halt of the winding being energized by a current substantially equal to the curent in the current transformer secondary 22 and the other halfY by a current substantially equal to the current in the current transformer secondary 23. rllhe resultant' edect of the whole winding is therefore substantially equal to one-halt of the vectorial sum of the currents in the current transformer secondaries 22 and 23 A and by reason of the turn ratio assumed, the

current appearing in the relay coil 26 is twice as great so that the relay 25 .is energized by a current substantially proportional to the vectorial sum ot the line currents whet-her one or both lines is or are in service.

Protective means embodying my invention is ot particular value where differential protection involving current transformers connected in series for normally circulating current is provided and it is desired to provide additional protection such that either ot two parallel lines alone may carry as much current as the two together and the vectorial sum carriedat any time should not exceed a predetermined value. This protective means is very simply and economically provided, since there is required but one additional inductive device and a relay whose adjustment does not have to be altered to correspond to the lines in service.v

While ll have shown and described my invention and one application thereof in considerable detail, l do not Adesire to be limited to .the enact arrangements and application shown, but seek to cover in the appended claims all those modifications that tall within the true spirit and scope of my invention. g What l claim as new and desire to secure by Letters Patent o/the United States is l. Protective means for controlling two parallel lines whereby either line alone may carry as much current as the two lines together, comprising current transformers respectively connected to be energized from the lines, a circuit comprising the secondaries of the current transformers connected in series for normally circulating current, an inductive winding connected in series in said circuit, a connection from the midpoint or" said winding to another point oi said circuit normally at substantially the same potentialfand a relay having a coil connected across said inductive winding, the construction and arrangement of parts being such that the relay is energized by a current substan-' tially proportional to the vectorial sum of the line currents.

2. In a prospective arrangement tor an electric system wherein two parallel lines are arranged to be controlled by circuit interrupters, means for controlling the operation of said interrupters comprising a relay and means for energizing the relay by a current derived from the line currents and substantially proportional to the vectorial sum thereof, comprising vcurrent transformers respectively connected to be energized from the lines, -a circuit comprising the secondaries of the current transformers connected in series for normally circulating current, an inductive winding connected in series in said circuit, a connection across said circuit from an intermediate point in said winding, said relay having a coil connected in circuit with/ said inductive winding.

3. A protective arrangement for two parallel lines comprising current transformers respectively connected to be energized fromn the lines, a circuit comprising the secondaries of the current transformers connected in series for normally circulating current, an inductive winding connected in series in said circuit, a connection from an intermediate point of said winding to another point or" said circuit normally at substantially the same potential, and a relay having a coil connected to be energized `from said inductive winding.

d. Protective means for controlling two parallel lines whereby either line alone may carry asmuch'current as the two lines together comprising a relay and means ior energizing said relay by a current derived Yfrom the line currents and substantially proportionalto the' vectorial sum thereof comprising current transformers respectively connected to be energized from the lines, a circuit comprising the secondaries ot the current transformers connected in series tornormally circulating current, stationary inductive means having, a winding connected in series in said circuit, and a connection from the midpoint oit said winding to another point on said circuit normally at substantially the same potential, said relay havi e a coil connected in circuit with said inductive means.

5. A 'protectivearrangement for two parallel lines comprising current transformers respectively connected to be energized from the lines, a circuit comprising the secondaries ot the current transformers connected in series for normally circulatingcurrent, stationary inductive means having a winding connected' in series in said circuit, a connection from an intermediate point of said winding to another point on the other sideoi said circuit'normally substantially the `same pollU tential, and an electroresponsive device contive means comprising a winding connected nected to be energized from said inductive in said circuit,a connection across said circuit 10 means. from an intermediate point of said winding,

6. A protectivearrangement for two parand an electroresponsive device connected to allel lines comprising transformers respecheU energized from said inductive means.

tively connected to be energized from the. In4 Witness whereof, I have hereunto set lines, ay circuit comprising the secondaries of my hand this 16th day of March, 1926.l f the transformers connected in series, induc- OLIVER C. TRAVER. 

